Method for producing globular articles



Feb. 13, 1951 KULP 2,541,165

METHOD FOR PRODUCING GLOBULAR ARTICLES Original Filed Feb. 15, 1947INVENTOR. MAUR/CE P. KULP Patented Feb. 13, 1951 METHOD FOR PRODUCINGGLOBULAR ARTICLES Maurice P. Kulp, Linwood, Pa., assignor to AmericanViscose Corporation, Wilmington, Dcl., a

corporation of Delaware Original application February 15, 1947, SerialNo. 728,788. Divided and this application February 4, 1948, Serial No.6,143

7 Claims. (CI. 18-48) This invention relates to the production ofglobular particles of regenerated cellulose, particularly from viscose.This application is a division of copending application Serial No.728,788, filed February 15, 1947.

Methods that have heretofore been employed for making globular particlesfrom viscose resulted generally in products which not only were far fromsphericity but were marred by numerous checks and fissures resultingfrom the in ability to prevent the development of gases within theglobule during regeneration and the in ability to prevent irregularshrinkage during regeneration, subsequent wet processing, and drying ofthe globules.

In accordance with the present invention these difiiculties aresubstantially completely avoided. This is accomplished by allowingdroplets of viscose to form in a gaseous atmosphere and fall into asubstantially non-regenerating bath from a height which is suificient toallow the droplet to assume a substantially spherical shape prior toentering the bath. The height required depends upon the size of dropletwhich can be varied by varying the size of orifice, the temperature ofthe viscose, or the pressure exerted on the viscose passing through theorifice. A droplet of a size which forms a particle of inch diameterrequires a drop of at least 6 feet,

.while smaller droplets will require less drop and larger ones a greaterdrop to allow the surface tension sufficient time to overcome thenonsphericity of a droplet of viscose having a viscosity of about 40(ball fall). After a short period in the non-regenerating bath (between/2 and minutes), the superficially coagulated structure is introducedinto a heated liquid of non-solvent, non-softening and nonacid characterin which coagulation and regeneration of the globules are completed.Suitable liquids for this purpose are hot aqueous salt solutions at atemperature below the boiling point of water.

After the globules are taken from the heated liquid, the by-products ofregeneration, such as alkaline and sulfur compounds, are in awatersoluble state and are merely leached out by introducing theglobules into water, preferably hot, for the desired period of time.Thereafter, the globules may be dried or, before drying, they may besoaked in a, plasticizer, such as glycerine, when a softened product isdesired. Shrinkage to any substantial extent can only occur during thedrying step of this procedure since the contact of the globules withacid is restricted to a minimum and the globules are maintained inwater-swelled condition thereafter until the drying stage. It has beenfound that the shrinkage that occurs during the drying of the globulesformed in accordance with the procedure of this invention is remarkablyuniform in character and substantially iso-tropic so that they undergolittle change in their original shape other than a diminution in duringthe drying.

The original shape of the globules formed de pends upon the height fromwhich the viscose droplets are allowed to fall into the acid bath. ifdropping heights are used which are considerably greater (more thanabout 20% greater) than the minimum needed to obtain sphericity, thesize of the droplet falling from the dropping orifice or jet does notdetermine the ultimate size of the product as in such cases, they tendto disrupt into numerou smaller particles which may have various sizes,and, in the extreme of conditicns, a powdered product results.

The sole figure the drawing illustrates one arrangement for executingthe invention.

As shown in the drawing, the viscose solution in a vessel 2 which may beprovided with a plunger 3 for exerting pressure thereon passes through adropping tube terminating in an orifice i. A receptacle 5 for thecoagulating bath is arranged beneath the hopper to receive the dropletsand preferably has a sloped bottom 6 to facilitate removal of theparticles roughly in their order of production.

The bath in the receptacle 5 may advantageously be an aqueous solutioncontaining 3 to 6% acetic acid and 15 to 20% sodium sulfate at 40 to 0.,and the particles are allowed sufficient contact therein to form a thincoagulated skin thereon. Then they are removed and placed in a 20%sodium sulfate solution in water at to C. or up to the boiling point ofwater. This bath is agitated and the treatment is carried on for aboutan hour. Finally, the pellets or granules are removed from the salt bathand introduced into a leaching vessel in which they are subjected for 8to 12 hours or longer to a fiow of hot water at 60 to- 7G G. or higher.This completes the purification of the pellets while substantiallypreventing any irregular shrinkage. The particles may remain in thisbath an indefinite period or they may be stored in cold or hot water foran indefinite period before ultimate drying. However, if convenient,drying may be performed directly after the leaching period of 8 to 12hours mentioned. Preferably, the humidity is controlled to preventirregular shrinkage.

The final products which may be of any size up to the order of inch indiameter approach true sphericity and are substantially free of checks,fissures, bubbles, creases and wrinkles. The unplasticized products arehard: and have a high dielectric constant. Because of thischaracteristic and the fact that the products are highly resistant tohydrocarbon oils'they may be used in conjunction with such oils forcooling electrical equipment, such as transformers. The

a substantially non-regenerating aqueous saltcontaining dilute acidbath, removingthe formed granules of viscose from the bath' after asupericial coagulation thereof, and introducing the superficiallycoagulated granules into a heated non-acid aqueous salt-containing bathincapable of softening the granules and having a tempera ture of atleast 60 C.

2. The method of making granular particles comprising regeneratedcellulose comprising the steps of allowing droplets of viscose tov fallthrough air into a substantially non-regenerating salt-containing bathcontaining acetic acid, removing the formed granules of viscose from thebath after a thin skin has been formed thereon,

introducing the superficially coagulated granules into a heated non-acidaqueous salt-containing bath incapable of softening the granules andhaving. a temperature of at least 60 C, and then leaching the granules;

3. The method. of making granular particles comprising regeneratedcellulose comprising the steps of allowing droplets of viscose to fallthrough the. air from asufficient height into a substantiallynon-regenerating salt-containing bath containing acetic acid to causethe droplets to assume a spherical shape before entering the bath,removing the formed granules of viscose from the bathafter a thinskinhas been formed thereon, introducing the superficially coagulatedgranules into a heated non-acid aqueous saltcontaining bath incapable ofsoftening the granules and having a temperature of at least 60 C.

4: The method of makin granular particles comprising regeneratedcellulose comprising the steps of allowing-droplets of viscose to fallinto a. non-regenerating bath consisting of sodium sulfate; acetic acid,and water, removing the formed granules of viscose from the bath afterav thin skinhaszbeien formed thereon, and introducing, the-superficiallycoagulated granules into a heated aqueous sodium sulfate solution havingatemperature of at least 60 C.

5. The method of making regenerated cellulose: globules: approachingsphericity in: shape comprising the steps of allowing viscosertoifallinthe form of individual drops'into a non-regencrating bath consistingof 10. to 20% sodiumsulfate, 3 to 6% acetic acid; andwater; removing theformed; globules from the bath after. a. thin skin has'been formedthereon, introducing the superficially coagulatedglobules into, a heatedbath consisting of sodium sulfate and-water havingatemperature of'atleast 60 C;

6; Themethod of claim 5- followed-by thestep of leaching. theparticlesin hot water, and drying: them.

'7'. The. method of" claim Gin which the-first bath is at about 40 to50C; andthe. subsequent paths are at temperatures of. 60 1301 99. 6.

MAURICE "P: KULP:

REFERENCES CITED I The following references are of record in the file ofthis patent:

UNITED STATES .PATENTS Number Name Date 2,249,745 Charch et a1 J'ul y222-1941 2,413,123 Underwood Dec. 24, 1946 2,465,343 Battista Mar. 291949

1. THE METHOD OF MAKING GRANULAR PARTICLES COMPRISING REGENERATED CELLULOSE COMPRISING THE STEPS OF ALLOWING DROPLETS OF VISCOSE TO FALL INTO A SUBSTANTIALLY NON-REGENERATING AQUEOUS SALTCONTAINING DILUTE ACID BATH, REMOVING THE FORMED GRANULES OF VISCOSE FROM THE BATH AFTER A SUPERFICIAL COAGULATION THEREOF, AND INTRODUCING THE SUPERFICIALLY COAGULATED GRANULES INTO A HEATED NON-ACID AQUEOUS SALT-CONTAINING BATH INCAPABLE OF SOFTENING THE GRANULES AND HAVING A TEMPERATURE OF AT LEAST 60* C. 